Implementing an RBL

In general, implementing an RBL provides the most immediate benefit
to reducing spam traffic. A good RBL implemented by your MTAs immediately
reduces spam by a minimum of 10 percent. In some cases, this number could
approach 50 percent.

You can use your RBL and Brightmail together. If Brightmail takes care
of 95 out of 100 emails for a certain IP address within some amount of time
you should add that IP address to your RBL. You can adjust the RBLs for Brightmail’s
false positives when you do your Brightmail analysis. That makes the RBL much
more proactive in handling a specific wave of spam.